coqpp's error messages are uninformative

[JasonGross]

Description of the problem

When I run coqpp on

DECLARE PLUGIN "foo"

VERNAC COMMAND EXTEND foo CLASSIFIED AS SIDEFF
| [ "Foo" ] -> { }
END

VERNAC COMMAND EXTEND Bar CLASSIFIED AS SIDEFF
| [ "Bar" ] -> { () }
END

I get

File "src/Util/plugins/foo.mlg", line 5, characters 58-59:
Error: Syntax error: operator expected.

Line 5 has only three characters, END, so I don't know what 58-59 are, and what is an operator, and why is it expected.

If I try inserting ;; after END, then I just get

File "src/Util/plugins/foo.mlg", line 5, characters 3-4:
Error: syntax error

What is the invalid syntax, and what's expected?

cc @ppedrot

Coq Version

59079a2

[JasonGross]

Also, "Error: Syntax error: operator expected." is a horrible error message for "type is a reserved keyword" (or something like that) (and it shows up on characters 75-79 of the line }).

{

open Stdarg

}

DECLARE PLUGIN "foo"

VERNAC COMMAND EXTEND Foo CLASSIFIED AS SIDEFF
  | [ "Foo" constr(type) ] -> {
    ()
  }
END

gives

File "src/Util/plugins/foo.mlg", line 12, characters 75-79:
Error: Syntax error: operator expected.

[SkySkimmer]

The error is actually from ocamldep, coqpp produces a .ml file without complaint.